1. Field of the Invention
The invention relates generally to valves and, more particularly, to the sealing of ball valves.
2. Description of Prior Art and Related Information
Various types of valves are used to control flow of fluids, such as liquid and gas, through pipes or flow lines. Most common types of valves include ball valves and plug valves. The fluids may be in a wide range of pressure, temperature, and viscosity. A sealing system is required to prevent pressurized fluids from escaping the valves, and particularly at gaps in the interconnections between pipes and valves. Conventional valves have relied on O-ring or square-ring or other shape seals that are made of elastomeric or polymeric materials such as rubber or polytetrafluoroethylene (PTFE, commonly under the trade name TEFLON®). Such elastomeric or polymeric materials need to be compressed to effectively seal the gaps.
For cryogenic applications, both liquid and gaseous phases of fluids are involved. In addition, the low temperature associated with cryogenic applications tends to cause the valve parts and pipes, which are usually made of metals, to contract, thus enlarging the gaps therebetween. And, conventional O-ring seals become less effective under low temperature because of the change in their elastomeric properties.